Subak is an ancient irrigation system which involves traditional and religious aspects in Bali. Regardless of its heritage value, its performance in distributing water for rice is necessary, in terms of water scarcity and food production issues. This study was conducted to assess the performance of Subak Ulumayu and Subak Sembung in 2018/2019. Several spatial dataset were processed using pySEBAL to generate biomass, ET, and T data. Results showed that rice consumed 968-1014 mm water, which resulted 4.87-4.93 tons rice/ha in this season. Most subfields showed relatively good performance, i.e. Relatively Water Deficit <0.2, adequacy >80%, and equity CV<10%, although Relatively Yield Deficit was high and efficiency was slightly low. According to those results, it can be concluded that both Subak irrigation systems are working properly to supply water for rice fields. However, there is a remained challenge to optimize the rice productivity to contribute for national food security.<br />